The invention relates to a method of and apparatus for receiving and handling core material, and, more particularly, to a method of and apparatus for stabilizing the cores taken within rubber sleeve core barrels.
It is generally the practice when drilling oil and gas wells to recover whole vertical sections of prospective geological formations at various depths in the drilling operation. This routine sampling is called coring and aids in determing the geological characteristics of the sub-structure. Such steps have, since the inception of deep hole drilling, been integral to proper drilling rig operations in the ultimate analysis of a particular area for oil and gas content. Consequently, coring devices have been developed for recovering columnar masses of core material from deep in the earth. The core materials are then brought to the surface for examination.
Prior art coring apparatus has included specially designed cutting heads in the form of hollow drill bits affixed to the end of elongated structures called core barrels. Conventional coring devices are generally comprised of stationary inner and rotatable outer barrels. The outer barrel rotates with the drill pipe and rotates the drill bit. As the formation is penetrated, the "core" is fed into the inner barrel. When a sufficient core sample has been taken and/or the inner barrel of the barrel is full, it is raised to the surface for subsequent analysis.
The conventional core barrel having been withdrawn from the well, is generally vertically suspended in the derrick above the rig floor for removal of the core. The most commonly utilized prior art methods and apparatus for recovering the core sample therefrom include an antiquated manual technique wherein the raw core sample is sectionally exposed and broken off. This less than optimal technique fostered the development of improved core recovery apparatus, among which has been the rubber sleeve core barrel.
Recovery of geological rock formations which are soft and unconsolidated in nature is greatly facilitated by core barrels which encase the core in a rubber sleeve as it is being bored. Such cores are generally about twenty feet in length and on the order of three inches in diameter. The original diameter of the generally heavy walled Neoprene rubber sleeve is less than three inches so that in its expanded capacity, it gives some measure of support to the core material contained therein. In this manner, the encased core may be removed from the suspended core barrel in one piece while substantially maintaining the physical integrity thereof.
Removal of the encapsulated core from the core barrel is generally effected while both are suspended from the derrick. First the core barrel is disassembled to expose the encapsulated core. The upper area of the rubber sleeve is then manually cut and wrestled to the floor of the rig. Similarly, the encapsulated core must generally be wrenched into numerous contortions in order to remove it from the rig. During these manual procedures the encapsulated core is subjected to blending, twisting and distortion, imparting physical strain to the core which inherently causes relative movement between rock grains and skeletons therein affecting physical properties such as permeability. Fragile rock skeletons may then collapse or become disoriented and repositioned as compared to their initially bored and received condition. Such alterations of the core configuration are particularly observable in friable formations where particles are loosely cemented together and fluid fills the spaces therebetween. Moreover, loosely consolidated formations are indigenous to areas in the Southern portion of the United States and Northern Mexico where satisfactory recovery of core samples is a must in effective oil and gas prospecting operations.
It would be an advantage therefore, to overcome the disadvantages of prior art encapsulated core recovery methods and apparatus by providing means for the immobilization and stabilization of the rock grains and skeletons contained therein prior to removal of the suspended core from the derrick and the handling associated therewith. The method and apparatus of the present invention are provided for just such a purpose. The encapsulated core is solidified through freezing while suspended in the derrick to allow for requisite handling without adversely affecting the physical properties thereof. In addition, the solidified core may also be rigidly encased in a casting medium to provide the desirable longitudinal rigidity thereto after the core thaws. In this manner the core is thereby prepared for transportation to a remote location for study and evaluation in its original condition.